The present invention relates to a non-impact printer and a print head for non-impact printer such as a LED head for electrophotographic printer and a thermal head.
FIG. 1 is a block diagram showing a conventional LED head 10 which comprises a plurality of light-emitting elements LD.sub.1 -LD.sub.2560 (only LD.sub.1 -LD.sub.4 are shown in FIG. 1) capable of printing at 300 dots per inch (DPI). SR.sub.1 -SR.sub.2560 (only SR.sub.1 -SR.sub.4 are shown in FIG. 1) are shift registers for sequentially shifting bit data signal DATA in synchronization with a clock signal CLK. LT.sub.1 -LT.sub.2560 (only LT.sub.1 -LT.sub.4 are shown in FIG. 1) are latches for latching the bit data signal DATA when the latch signal LOAD is inputted. G.sub.1 -G.sub.2560 (only G.sub.1 -G.sub.4 are shown in FIG. 1) are gate elements, Tr.sub.1 -Tr.sub.2560 (only Tr.sub.1 -Tr.sub.4 are shown in FIG. 1) are transistors as switching elements, r.sub.1 -r.sub.2560 (only r.sub.1 -r.sub.4 are shown in FIG. 1) are protective resistors, and V.sub.D is a power supply line. When high level signals from the latches LT.sub.1 -LT.sub.2560 are applied to the gate elements G.sub.1 -G.sub.2560 and the low level drive signal STB is inputted to the gate elements G.sub.1 -G.sub.2560 for executing printing, high level inputs are applied to the bases of the switching elements Tr.sub.1 -Tr.sub.2560. At this time, the switching elements Tr.sub.1 -Tr .sub.2560 turn to the on state, a drive current flows in the light-emitting elements LD.sub.1 -LD.sub.2560, and then the light-emitting elements LD.sub.1 -LD.sub.2560 emit light.
However, there are variations in the individual characteristics of the light-emitting elements LD.sub.1 -LD.sub.2560 and the switching elements Tr.sub.1 -Tr.sub.2560. Consequently, as indicated at the lower side of FIG. 2, the individual light intensity E.sub.1 -E.sub.2560 (only E.sub.1 -E.sub.6 are shown in FIG. 2) of the light-emitting elements LD.sub.1 -LD.sub.2560 are different and as indicated at the upper side of FIG. 2, the sizes of the printed dots d.sub.1 -d.sub.2560 (only d.sub.1 -d.sub.6 are shown in FIG. 2) are not uniform, thereby resulting in deterioration of printing quality.